In recent years, trend of high compression and high supercharging in internal combustion engines is advanced in order to improve thermal efficiency (for example, see Japanese Patent Application Laid-Open (kokai) No. 2014-239015). Therefore, spark plugs are required to advantageously exhibit ignitability even when the spark plugs are mounted to such internal combustion engines.
High compression or high supercharging in an internal combustion engine may increase, for example, electric energy to be supplied to a spark plug, as compared to general energy in order to cause stable ignition by the spark plug. However, when the electric energy to be supplied to the spark plug is increased, electrode wear of the spark plug becomes severe while ignitability is improved. Therefore, a spark plug that has an excellent wear resistance while maintaining ignitability even when high electric energy is supplied to the spark plug, is required.
The present invention is made in order to address the aforementioned problem, and can be embodied in the following modes.